1. Field of the Invention
The invention relates to planar coils and, more particularly, to planar coils especially adapted for use in a force-producing device such as a de-icer.
2. Description of the Prior Art
The accumulation of ice on aircraft wings and other structural members in flight is a danger that is well known. As used herein, the term "structural members" is intended to refer to any aircraft surface susceptible to icing during flight, including wings, stabilizers, engine inlets, rotors, and so forth. Attempts have been made since the earliest days of flight to overcome the problem of ice accumulation. While a variety of techniques have been proposed for removing ice from aircraft during flight, these techniques have had various drawbacks that have stimulated continued research activities.
One approach that has been used extensively is so-called mechanical de-icing. In mechanical de-icing, the leading edges of structural members are distorted in some manner so as to crack ice that has accumulated thereon for dispersal into the airstream. A popular mechanical de-icing technique is the use of expandable tube-like structures that are periodically inflatable. Inflation of the structures results in their expansion or stretching by 40% or more. Such expansion typically occurs over approximately 2-6 seconds and results in a substantial change in the profile of the de-icer, thereby cracking accumulated ice. Unfortunately, expansion of the devices can negatively influence the airflow passing over the aircraft structure. Also, they are most effective when ice has accumulated to a substantial extent, approximately 0.25 inch or more, thereby limiting their effectiveness. Desirably, ice removal would be accomplished long before accumulations approximating 0.25 inch have been attained.
A more recent mechanical de-icing technique utilizes internal "hammers" to distort the leading edges of structural members. Such an approach is exemplified by U.S. Pat. No. 3,549,964 to Levin et al., wherein electrical pulses from a pulse generator are routed to a coil of a spark-gap pressure transducer disposed adjacent the inner wall of the structural member. The primary current in the coil induces a current in the wall of the structural member and the magnetic fields produced by the currents interact so as to deform the member.
U.S. Pat. Nos. 3,672,610 and 3,779,488 to Levin et al. and 4,399,967 to Sandorff disclose aircraft deicers that utilize energized induction coils to vibrate or torque the surface on which ice forms. Each of these devices employs electromagnetic coils or magneto-restrictive vibrators located on the side of the surface opposite to that on which ice accumulates. In U.S. Pat. No. 3,809,341 to Levin et al., flat buses are arranged opposite one another, with one side of each bus being disposed adjacent an inner surface of an ice-collecting wall. An electric current is passed through each bus and the resulting interacting magnetic fields force the buses apart and deform the ice-collecting walls.
A more recent approach is shown by U.S. Pat. No. 4,690,353 to Haslim et al. In the '353 patent, one or more overlapped flexible ribbon conductors are imbedded in an elastomeric material that is affixed to the outer surface of a structural member. The conductors are fed large current pulses from a power storage unit. The resulting interacting magnetic fields produce an electro-expulsive force that distends the elastomeric member. The distension is almost instantaneous when a current pulse reaches the conductors, and is believed to be effective in removing thin layers of ice. Although the device disclosed in the '353 patent is believed to be an improvement over previous mechanical de-icing techniques, certain drawbacks remain. One of the drawbacks relates to the direction of current flow in adjacent electrically conductive members. It is believed that the current flow disclosed in the '353 patent produces inefficiencies that significantly restrict the effectiveness of the device.
The Electro-Repulsive Separation System Patent discloses a device that is an improvement over that disclosed in the '353 patent. In the Electro-Repulsive Separation System Patent, the electrically conductive members are arranged with current flow in a common direction in a conductor layer such that a greater electro-expulsive force can be generated than with the serpentine configuration disclosed in the '353 patent. Also, the Electro-Repulsive Separation System Patent teaches the delivery of a current pulse of predetermined magnitude, shape and duration that provides more effective de-icing action.
Despite the advances taught by the prior art, particularly the Electro-Repulsive Separation System Patent, there remains a need for a de-icer that provides effective de-icing action. A particular concern relates to the electrically conductive members that are used with the prior devices. It is desired to provide coils that are as thin as possible, while being relatively inexpensive and easy to manufacture. Desirably, any such coils would have a very high efficiency, that is, they would generate more force than prior electrically conductive members for a given current input. The coils also desirably would permit a small or large area of force production as desired for a de-icer construction.